The present invention relates to interconnections for semiconductor integrated circuits, and more particularly to optical interconnections which cause a multiplicity of elements in semiconductor integrated circuits to be activated or operated.
In the hitherto known semiconductor integrated circuits, wirings or interconnections for transferring clocks, timing signals or the like are realized by diffused resistive layers, metal layers (made of, for example, aluminum) or the like formed on a semiconductor chip. With such electrical interconnections, however, delays of signal transfer take place due to electrostatic capacitances associated with the electrical interconnections, thereby resulting in a hindrance to improvement in the operation speed of an integrated circuit.
In order to solve such a problem, an optical interconnection system using light for signal transfer has been proposed, as disclosed by, for example, J. W. Goodman et al, "Optical Interconnections for VLSI Systems", Proc. of the IEEE, Vol. 72, No. 7, pp. 850-866, July 1984. In the optical interconnection system, an optical signal is transferred through the propagation in a free space or via optical fibers or optical waveguides, thereby allowing the signal transfer at a very high speed which is equal to the propagation speed of light in such a medium.
FIG. 1 shows an example of the optical interconnection system, disclosed by the above-mentioned Goodman et al's article, in which light propagating in a free space is used. Referring to the figure, light as an optical signal emitted from a light source 110 is collimated by a lens 130 to irradiate a semiconductor integrated circuit chip 140. Light receiving elements 120 to 125 formed in the integrated circuit chip 140 receive the optical signals to convert them into electrical signals. If such optical signals are clock signals for logic circuits formed in the integrated circuit chip, the timings of electric clock signals reproduced or regenerated at any points on the chip would completely coincide with each other. This provides an advantage that the occurrence of a timing jitter resulting from the propagation delays which may take place in the case of electrical interconnections can be prevented.
In the above described conventional example of the optical interconnection system, however, since the entire upper surfaces of the semiconductor integrated circuit is uniformly irradiated, some photoelectrons are generated by optical excitation in the whole integrated circuit including the light receiving elements. Such generated photoelectrons can have an adverse influence, large and small, on the characteristics of transistors or diodes included in the integrated circuit, resulting in inferior operating characteristics of the integrated circuit and/or erroneous operation thereof.
As to the light illuminating the upper surface of the semiconductor integrated circuit, the effective light portion or a light portion incident on the light receiving elements 120 to 125 is extremely small since the areas of the light receiving elements are limited because of improvement of the integration degree. Therefore, the efficiency of utilization of light is poor.
Further, the above-described conventional example of the optical interconnection system assumes simultaneous activation of all the light receiving elements. Namely, no consideration is given with respect to selective activation of the light receiving elements.